PERCHLORATE REMOVAL PROCESS

Abstract: A process for removing perchlorate ions from waste water using KCl is disclosed. In the process, waste perchlorate is concentrated by water evaporation in a stripping tower. Ammonia and volatile organics are removed during the concentrating step. Potassium chloride (KCl) is added to the concentrated perchlorate solution to form potassium perchlorate (KClO4), and the reaction mixture is cooled to effect crystallization of the potassium perchlorate. The crystallization liquor is removed by centrifuge or filter press and may be further treated as part of an overall waste water treatment system.

Description: PERCHLORATE REMOVAL PROCESS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to water treatment processes. More particularly, the present invention is directed to a process for removing perchlorate ions from waste water. 2. Technology Background Ammonium perchlorate (abbreviated "AP", having the chemical formula NH 4 C10 4 ) is a common waste stream ingredient in the processing and reclamation of solid rocket propellants. Because solid rocket motors often include 60% AP, water used to wash and clean rocket motor processing facilities and equipment typically contain up to about 100,000 parts-per-million (ppm) AP. There are three approaches that have been used in the industry for disposing of waste streams containing AP. In the first approach, the waste water is treated to remove high energy materials, such as NG, HMX or RDX, and the waste stream is discharged for treatment by a municipal or privately owned water treatment facility. The perchlorate is not treated but is diluted. In the another approach, a third party, such as a slurry explosive company, is paid to evaporate the water from the waste stream leaving a concentrated AP slurry capable of use as in the mining industry as a slurried explosive. There is also a patented Bio-digestion process for low level treatment of AP. There still remains a need in the art for a process of removing AP from waste streams. Such a process for removing perchlorate ions from waste water is disclosed and claimed herein. SUMMARY OF THE INVENTION The invention is directed to a process for removing perchlorate ions from waste water. In the process of the present invention, waste perchlorate is concentrated by water evaporation, preferably in a stripping tower. During the concentrating step, ammonia and volatile organics are also removed. Solid potassium chloride (KCl) is then added, and the reaction mixture is cooled to effect crystallization of potassium perchlorate (KC10 4 ) . The crystallization liquor is removed by centrifuge or filter press and may be further treated as part of an overall waste water treatment system. The treatment chemistry is shown below: Na + [C10 4 ]' + KCl → KC10 4 + Na CI Ca Ca Mg Mg NH 4 NH 4 Etc Etc DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to a process for removing perchlorate ions from waste water. In the process of the present invention, waste perchlorate is concentrated by water evaporation. Stripping towers and thin film evaporators are two possible devices for concentrating the waste perchlo¬ rate stream. The currently preferred method of concentrating the waste perchlorate stream is the use of a stripping tower. The use of the stripping tower facilitates the removal of ammonia. Stripping towers and their operation are well known to those skilled in the art. The size and capacity of the stripping tower used will depend on the quantity of waste perchlorate that must be processed. In general, stripping towers are filled with packing which creates a large surface area within the tower. The heated fluid is introduced at the top of the tower, usually by spraying. As the fluid flows over the packing material, air is blown up from the bottom of the tower. Air blowing from the bottom of the tower drives off ammonia and evaporates water. It is important that the water temperature and flow rate be balanced against the air flow rate to prevent flashing or drying within the tower. In the present case, the perchlorate waste stream is heated to a temperature greater than 150°F, preferably greater than 200°F, and most preferably about 240°F. The higher the temperature, the faster the evaporation and the more soluble is the KCl. For a typical tower size of 4 feet x 6 feet, a water flow rate of about 60 gallons/minute at 240°F balances an air flow rate of about 3000 cubic feet/minute. As used herein, 1 pound equals 453.593 grams, 1 foot equals 0.3048 meters, 1 gallon equals 3.785 liters, and 1 cubic foot equals 28.32 liters. As used herein, temperature expressed in degrees Fahrenheit may be converted to degrees Centigrade by subtracting 32 and multiplying the result by 5/9. Concentrated waste perchlorate from the stripping tower passes into a reactor vessel. Potassium chloride (KCl) is then added to the hot concentrated waste perchlorate. The amount of KCl added depends upon the concentration of the waste perchlorate. A stoichiometric excess of KCl is preferred; however, too much excess KCl results in additional potassium and chloride ions which ultimately must be accounted for in the waste stream. It is currently preferred that the perchlorate concentration be reduced from about 250,000 to 100,000 ppm to a level below 6000 ppm. To achieve this end concentration, a stoichiometric excess of 2 KCl is added to the waste perchlorate. Once the KCl is added, potassium perchlorate (KC10 4 ) immediately begins to precipitate. Since the solubility of potassium perchlorate is temperature dependent, the reaction mixture is preferably cooled to cause the maximum crystalliza¬ tion of potassium perchlorate. Best results have been observed when the crystallizer temperature is maintained below about 60°F and preferably below 40°F. A waste perchlorate slurry passes from the reactor vessel to a crystal dewatering unit. The dewatering device is a centrifuge, filter press or another filtration device. Such dewatering devices are well known in the art. The crystalli¬ zation liquor may be further treated as part of an overall waste water treatment system to remove ammonia, heavy metals, organic, suspended solids and or other contaminants and other waste materials. The chemical reaction governing the treatment process of the present invention is shown below: Na + [C10 4 ]- + KCl KC10 4 + Na CI Ca Ca Mg Mg NH 4 NH 4 Etc Etc There are important advantages one obtains using KCl in the perchlorate removal process. For instance, KCl is relatively noncorrosive, nontoxic, nonhazardous, and easy to work with. No acid neutralization or pH modification is required. KCl is a granular solid much like table salt which can be added directly without dilution of the concentrated perchlorate solution. This is more efficient and results in a higher yield of KC10 4 . Since the addition of KCl does not affect the pH of the solution, it can be added until the desired level of perchlo- rate concentration is reached, without the corrosion problem associated with high pH levels. The ability to drive the precipitation reaction to lower residual perchlorate levels using KCl is a significant advantage over the use of KOH. The amount of KCl required to obtain a desired level of perchlorate concentration is presented in Equation 1. C10 4 Concentration (ppm) * 8.3 x 10"* •= pounds KCl Eq. 1 The following is an example of a typical operation cycle. Feed Stream C10 4 concentration = 17060 ppm Gallons concentrated = 1750 Time to concentrate = 9.2 hrs Gallons concentrated solution reacted = 150 gals Pounds of KCl add = 242 lbs. Pounds of KP (moist) produced = 325 lbs Filter press filtrate C10 4 concentration = 333 ppm From the foregoing it will be appreciated that the present invention provides a perchlorate ion removal process which is not hazardous or corrosive and which does not require pH neutralization. The present invention further provides a perchlorate ion removal process which does not dilute the perchlorate solution, but results in high perchlorate yield. The process also lends itself to the removal of ammonia from the stream. The invention may be embodied in other specific forms without departing from its essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope. What is claimed is:

Claims: 1. A process for removing perchlorate ions from waste water comprising: (a) concentrating a waste perchlorate solution containing perchlorate ions; (b) adding potassium chloride (KCl) to the concentrated waste perchlorate solution to form potassium perchlorate (KC10 4 ) ; (c) effecting crystallization of the potassium perchlorate; and (d) separating the crystallized potassium perchlorate from the waste perchlorate solution. 2. A process for removing perchlorate ions as defined in claim 1, wherein the waste perchlorate solution is concentrated by water evaporation. 3. A process for removing perchlorate ions as defined in claim 1, wherein the waste perchlorate solution contains ammonium perchlorate and wherein the concentrating step further includes the step of removing ammonia and volatile organics from the waste perchlorate solution. 4. A process for removing perchlorate ions as defined in claim 1, wherein the concentrating step is accomplished by heating the waste perchlorate solution. 5. A process for removing perchlorate ions as defined in claim 4, wherein the concentrating step is accomplished in a stripping tower with a liquid inlet temperature maintained above about 150°F. 6. A process for removing perchlorate ions as defined in claim 4, wherein the concentrating step is accomplished in a stripping tower with a liquid inlet temperature maintained above about 200°F. 7. A process for removing perchlorate ions as defined in claim 4, wherein the waste perchlorate solution is cooled to effect crystallization of the potassium perchlorate. 8. A process for removing perchlorate ions as defined in claim 7, wherein the waste perchlorate solution is maintained at a temperature below about 60°F during the crystallization of the potassium perchlorate. 9. A process for removing perchlorate ions as defined in claim 7, wherein the waste perchlorate solution is maintained at a temperature below about 40°F during the crystallization of the potassium perchlorate. 10. A process for removing perchlorate ions as defined in claim 1, wherein the crystallized potassium perchlorate is separated from the waste perchlorate solution by centrifugation. 11. A process for removing perchlorate ions as defined in claim 1, wherein the crystallized potassium perchlorate is separated from the waste perchlorate solution by filter press. 12. A process for removing perchlorate ions as defined in claim 1, wherein the potassium chloride is a granular solid. 13. A process for removing perchlorate ions from waste water comprising: (a) concentrating a waste perchlorate solution by water evaporation in a stripping tower, wherein the waste perchlorate solution is heated to an inlet temperature greater than about 150° and wherein ammonia and volatile organics are removed from the waste perchlorate solution during the concentrating step; (c) adding potassium chloride (KCl) to the hot concentrated waste perchlorate solution to form potassium perchlorate (KC10 4 ) ; (d) cooling the waste perchlorate solution to a temperature below about 60°F to effect crystallization of the potassium perchlorate; and (e) separating the crystallized potassium perchlorate from the waste perchlorate solution. 14. A process for removing perchlorate ions as defined in claim 13, wherein the crystallized potassium perchlorate is separated from the waste perchlorate solution by centrifugation. 15. A process for removing perchlorate ions as defined in claim 13, wherein the crystallized potassium perchlorate is separated from the waste perchlorate solution by filter press. 16. A process for removing perchlorate ions as defined in claim 13, wherein the waste perchlorate solution is heated to an inlet temperature greater than about 200°F. 17. A process for removing perchlorate ions as defined in claim 13, wherein the waste perchlorate solution is maintained at a temperature below about 40°F during the crystallization of the potassium perchlorate. 18. A process for removing perchlorate ions as defined in claim 13, wherein the potassium chloride is a granular solid.

Inventors: MOWER GLENN L, MOWER, GLENN, L.
Applicants: THIOKOL CORP, THIOKOL CORPORATION
Application year: 1994
Main classification: C01D13
IPC codes: A62D3, A62D101, C01B11, C02F1, C02F101, C06B21